1. Field of the Invention
This invention relates to a photo-electric conversion device having a photo-electric conversion section.
2. Description of Prior Arts
The photoelectric conversion type information processing device having a solid state photoelectric conversion section is applicable to a television image pick-up device, an input device for facsimile, digital copier, or other reading devices for characters, picture images, etc., the development of which has progressed remarkably in recent years.
Such photoelectric conversion type information processing device includes a group of image elements having a photoelectric conversion function, and a circuit having a scanning function to take out an electric signal output from the image element group in the form of a time sequential arrangement. For such information processing device, there are various types such as one including a photo-diode and MOS FET (Metal Oxide Semiconductor--Field Effect Transistor (hereinafter abbreviated as "MOS type")) as constituent elements, or one including the so-called CTD (Charge Transfer Device) such as CCD (Charge Coupled Device) and BBD (Bucket Brigade Device), and so on as the constituent elements.
However, since the MOS type and CTD use a mono crystalline silicon wafer (hereinafter abbreviated as "C-Si") as the substrate, the area of the light receiving surface of the photoelectric conversion section is inevitably restricted by the size of the C-Si wafer. In other words, at the present stage, it is only possible to manufacture the C-Si wafer having a size of a few inches or so at best in consideration of uniformity in the entire region of such wafer. On account of this, the light receiving surface of the photoelectric conversion element cannot be larger than the size of the C-Si substrate in the photoelectric conversion type information processing device using such C-Si wafer and including MOS type or CTD as its constituent element.
Accordingly, when the information processing device having the photoelectric conversion section, the light receiving surface of which has such limited area, is used as the input device for the digital copier, for example, it is inevitably necessary that an optical system having a large image reduction ratio be interposed between an image original to be reproduced and the light receiving surface so that an optical image of the image original may be formed on the light receiving surface through the optical system. In this case, however, there exist technical restrictions against increase in image resolution to be described in the following.
When an image original in A4 size is to be reproduced with the photoelectric conversion section having its image resolution of, for example, 10 lines/mm and a length of the light receiving surface in the longitudinal direction of 3 cm, the optical image of the image original to be focussed on the light receiving surface is reduced to about 1/6.9 with the consequence that the substantial image resolution of the photoelectric conversion section to the A4 size image original reduces to about 1.5 lines/mm. Thus, the substantial image resolution of the photoelectric conversion section lowers at a rate of (size of the light receiving surface)/(size of the image original) according as the size of the image original to be reproduced becomes larger.
In order, therefore, to solve this problem in this type of information processing device, there is required a manufacturing technique for increasing the image resolution of the photoelectric conversion section. However, for such high resolution to be obtained with such limited small area, the manufacture of the photoelectric conversion section should be so conducted that its integration density may be made extremely high and its structural elements may be free from any defect. Such manufacturing technique, however, has its own limitation.
On the other hand, there has been proposed a new system, in which a plurality of photoelectric conversion sections are arranged in such a manner that the length of the entire light receiving surface in its lengthwise direction and the length in the scanning direction of the maximum size of the image original to be reproduced may be in a one-to-one relationship, and that the optical image of the image original focussed on the light receiving surface is divided into small fractions corresponding to the number of the photoelectric conversion sections, thereby preventing substantial lowering of the image resolution.
Even such system, however, has some inconveniences to be described as follows. That is, when a plurality of photoelectric conversion sections are arranged, there inevitably occur those boundary regions where no light receiving surfaces are present between adjacent photoelectric conversion sections, as the result of which the light receiving surfaces are lacking in continuity, when viewed generally, and the optical image of the image original to be focussed is split, and the portions of the image original at these boundary regions are not forwarded to the photoelectric conversion section as the input signal. In this consequence, the reproduced image has such incompleteness in its image-formation that it includes whitened lines in some parts thereof, or the image portions where those white lines to be formed are removed and the entire portions are joined together. Also, the optical image which has been focussed on the plurality of light receiving surfaces in division is an optically reversed image on each of the light receiving surfaces, so that the overall image differs from the optically reversed image of the image original. Accordingly, reproduction of the optical image focussed on the light receiving surface, as it does not lead to reproduction of the image original.
Thus, it is extremely difficult with the photoelectric conversion type information processing device provided with the photoelectric conversion sections to reproduce informations with high resolution, since its light receiving surface is small in area. It has therefore been desired to have such information processing device provided with the photoelectric conversion section having the light receiving surface of a sufficiently large area which does not necessitate size-reduction in the image original and having excellent image resolution. In particular, for the input device facsimiles and digital copiers, or the reading device for characters and images on the image original, the photoelectric conversion type information processing device should be indispensably provided with photoelectric conversion sections having a light receiving surface equal in size to the image original for reproduction and being capable of faithfully reproducing the image original without lowering the image resolution required of the image as reproduced.